# SMS:RMA2 Boundary Conditions

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## Assigning Boundary Conditions

Boundary conditions are generally defined on nodestrings but may also be defined on nodes or elements. The default boundary condition is a closed boundary (no flow).

## Deleting Boundary Conditions

Boundary conditions are removed using the menu command *RMA2* |** Delete BC**.

## Nodal Boundary Conditions

*Boundary Condition Type*

*None**Water Surface Elevation*

- A water surface elevation boundary condition is assigned to the selected nodestring. This boundary condition is normally located at the tailwater location. However. RMA2 does sometime edit the water depth at the exit boundary to satisfy the finite element equations.

*Velocity Components**Unit Flowrate**No Slip Condition*

*Boundary Angle*

- Specify Flow Direction
- Perpendicular into Boundary
- Perpendicular out of Boundary
- Specified angle

*Optional Parameters*

- Water Density
- Include in node summary file

*Boundary Condition Value*

- Constant
- Transient

## Nodestring Boundary Conditions

* Boundary Condition Type *

*None*

- No boundary condition is assigned to this nodestring.

*Specified Flow Rate*

- A flow rate boundary condition is assigned to the selected nodestring. It is the most popular way to provide a total flow across a particular continuity line. The total flow (cubic units per second), flow angle (degrees from positive x-axis) and distribution factor can be specified.

*Water Surface Elevation*

- A water surface elevation boundary condition is assigned to the selected nodestring. This boundary condition is normally located at the tailwater location. (However RMA2 does sometime edit the water depth at the exit boundary to satisfy the finite element equations.)

*Reflecting Boundary*

- Considered an advanced feature – for more information see the "Boundary Permeability (Reflection/Absorption)" section on page 99 of the Users Guide to RMA2 version 4.5.

*Rating Curve*

- A rating curve can also be defined by selecting the
**Options...**button.

- A rating curve can also be defined by selecting the

*Flow Rate*

- Constant
- Transient

*Boundary Reflection*

- Steady state water surface
- Tidal storage surface area

*Flow Direction*

- Degree CCW from positive X axis
- Perpendicular to boundary

*Advanced Options*

- Make this nodestring the "Total Flow" nodestring
- Specify vorticity

*Flow Distribution*

- A real number between 0.0 and 1.0, that is used to weight the nodal x and y velocity components according to the nodal depths and friction across the continuity line.

## Element Boundary Conditions

This dialog consists of three tabs.

*Inflow*– Allows assigning inflow to elements. The inflow can either be a constant value or transient.*Roughness*– Allows overriding global roughness values for the selected elements. A specific roughness value can be entered or roughness by depth can specified.*Advanced*– Contains options to specify marsh porosity, wind, or rainfall values for the selected element.

## Extract Nodal Boundary Conditions

This dialog is reached through the *RMA2* | **Extract Nodal BC** command. It is only available with dynamic simulations—defined in the *RMA2 Model Control* dialog.

*Boundary Condition Type*- "None"
- "Water surface elevation"
- "Velocity"
- "Unit-Flow"

*Specify Flow Direction**Perpendicular info boundary**Perpendicular out of boundary**Specified Angle*

**Extract**

**View Extracted**

## Related Topics

SMS – Surface-water Modeling System | ||
---|---|---|

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Riverine/Estuarine Models: | AdH • HEC-RAS • HYDRO AS-2D • RMA2 • RMA4 • SRH-2D • TUFLOW • TUFLOW FV | |

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